[RESEND][PATCH v31 2/9] sched/core: Don't steal a proxy-exec donor

From: Vasily Gorbik <[email protected]>

try_steal_cookie() avoids stealing src->core_pick and src->curr before
moving a task with the same cookie via move_queued_task_locked().

With proxy-exec, src->donor is the current scheduling context and may
differ from src->curr. Stealing it migrates a task that the source rq
still treats as current, leaving src's scheduler state for that task
stale. For CFS this means cfs_rq->curr points at the stolen entity,
and the next pick on the source rq hits the WARN_ON_ONCE in
put_prev_entity().

Commit 7de9d4f94638 ("sched: Start blocked_on chain processing in
find_proxy_task()") tweaked the fair class logic so that the donor task
isn't migrated away while we're running the proxy. Do it similarly for
try_steal_cookie() and skip src->donor as well.

Fixes: 7de9d4f94638 ("sched: Start blocked_on chain processing in find_proxy_task()")
Signed-off-by: Vasily Gorbik <[email protected]>
Signed-off-by: John Stultz <[email protected]>
---
Cc: Joel Fernandes <[email protected]>
Cc: Qais Yousef <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Juri Lelli <[email protected]>
Cc: Vincent Guittot <[email protected]>
Cc: Dietmar Eggemann <[email protected]>
Cc: Valentin Schneider <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Ben Segall <[email protected]>
Cc: Zimuzo Ezeozue <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Waiman Long <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Cc: Metin Kaya <[email protected]>
Cc: Xuewen Yan <[email protected]>
Cc: K Prateek Nayak <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Daniel Lezcano <[email protected]>
Cc: Suleiman Souhlal <[email protected]>
Cc: Andrea Righi <[email protected]>
Cc: kuyo chang <[email protected]>
Cc: hupu <[email protected]>
Cc: [email protected]
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 96226707c2f61..e7074ba54a91f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6474,7 +6474,7 @@ static bool try_steal_cookie(int this, int that)
 		return false;
 
 	do {
-		if (p == src->core_pick || p == src->curr)
+		if (p == src->core_pick || p == src->curr || p == src->donor)
 			goto next;
 
 		if (!is_cpu_allowed(p, this))
-- 
2.55.0.654.g21b8a5bc05-goog